Vigorous Exercise Can Be Problematic When Trying to Prevent Atrial Fibrillation

The risk with extremes can be seen in many aspects of our lives. It is harder to understand with exercise; something that we do to become more fit and live longer. Most who are very active in exercise hope that there is a linear response curve — the more exercise we put in, the better the dividends we receive in health and longevity.

This isn’t always the case, shows a new study of athletes and atrial fibrillation just out this month.

With Exercise, Either Extreme is Risky

In my prior column about exercise entitled “Exercise, Is More Really More?” I presented a few concepts. First, was a health outcome response called a “U” shaped curve. This curve indicates a higher risk of a particular health outcome at both ends of the certain activity or therapy. Weight and exercise are two examples.

In my previous column regarding weight, a U-shaped curve was also presented. In this column higher mortality rates were seen in both underweight and overweight people — with the lowest risk someplace in the middle. For exercise, there was also a U shaped curve. People who exercised the least and most had the worse outcomes as far as developing an abnormal heart rhythm called atrial fibrillation. In some studies as well, mortality risks were similar, being somewhat higher in the low exercise group and the high exercise group with the lowest risk someplace in the middle.

With mortality however, the cause of death between those with low activity and high activity were different, with the low activity level people having more heart disease-related deaths.

Athletes at the Heart Clinic

I see a number of very highly skilled endurance athletes in my heart clinic. They often go from marathon to triathlon to 100-mile bike race. They are amazingly fit people. The reason they see me is typically for the treatment of atrial fibrillation, an abnormal heart rhythm involving the upper heart chambers.

The association between atrial fibrillation and exercise intensity has been well described. As a scientific community we don’t know exactly why the association exists. We know that the risk of atrial fibrillation goes up in people that have lower resting heart rates, those athletes that participate in multiple races per year, and those athletes that have the best times in their races. Largely we know that atrial fibrillation occurs in the most fit even amongst the athletes. The reasons that this may occur is wear and tear on the heart from daily workouts. Here, the heart rate is maintained at a very fast level and sees changes in the autonomic nervous system that tend to provoke tissues responsible for generating atrial fibrillation. A personality that tends to allow excellence in endurance athletics also increases stress response on the heart. Herbal and nonherbal supplements used to improve endurance and recovery may increase abnormal heart rhythm risk.

What is interesting is that traditional risk factors for atrial fibrillation in these athletes are largely reduced or eliminated — such as high blood pressure, obesity, sleep apnea, etc. So mechanisms of why atrial fibrillation occurs are somewhat unique to this population of people.

One of the questions that these athletes often ask is: If their lifestyle and pursuit of fitness resulted in atrial fibrillation, then what should they do?

In general, the lifestyle reduces other heart risk factors and improves quality of life, so I don’t have a reason to recommend they stop. In fact, I do not know if stopping the exercise and allowing longer periods of heart recovery and increasing the resting heart rate may reverse the process. However, a recent study shed light on this subject and may provide a way to understand the next steps if atrial fibrillation develops.

Clinical Studies on Fitness and the Heart

The study looked at the impact of levels of fitness at different ages in a large number of men. In this study, Drca and colleagues from the Karolinska University Hospital, in Stockholm, Sweden, collected information about physical activity from 44,410 Swedish men from the ages of 45-79 who did not have atrial fibrillation. Researchers followed the men for an average of 12 years. They separated the men into groups by their vigorous exercise level:

Less than 1 hour per week

1-2 hours per week

2-3 hours per week

4-5 hours per week

More than 5 hours per week

The authors found that if men developed a pattern of exercise of >5 hours per week, then their risk of atrial fibrillation was 19 percent higher than those who exercise <1 hour. It was a classic “U” shape curve with the lowest risk at 2-3 hours per week. The risk was highest in those that start >5 hours of vigorous exercise by the age of 30.

What they found next was, to me, the most important finding. In men who exercised >5 hours per week at age 30 and quit exercising later in life or regressed to <1 hour per week, the atrial fibrillation risk increased further to 49 percent. The increased risks remained even when accounting for all types of heart disease and heart disease risk factors; diabetes, high blood pressure, and being a smoker.

These authors made a second important observation. They found that leisure activity of walking or cycling did not increase risk, even if it was over 60 minutes a day. In fact, walking over 1 hour per day was associated with a 13 percent decrease in atrial fibrillation. This lower risk of atrial fibrillation was seen in almost all of the groups and was independent of what age the activity was started. In fact, becoming more active with low-moderate intensity exercise helped lower all traditional risk factors of heart disease as well as atrial fibrillation.

Advice on Exercise to Protect Your Heart

What are the take home points? First, as the authors state very nicely, “several conditions, such as aging, hypertension, heart failure, valvular heart disease and diabetes are associated with atrial fibrillation. However, in addition to these well-known risk factors for atrial fibrillation, vigorous long-time physical activity seems to increase the risk for atrial fibrillation”.

Exercise duration matters. The duration of exercise intensity was a significant contributor to atrial fibrillation. This supports the possibility that atrial fibrillation, in athletes, is a consequences of the wear and tear on the upper heart chamber that produces small injuries and fibrosis causing the abnormal rhythms.

Inactivity increases heart risks. Next, physical inactivity is also a significant risk that is independent of age — so people need to be active and adopt active lifestyles. Walking and cycling (low-moderate exercise) are very protective of heart disease, including atrial fibrillation.

Going from too much to too little exercise is risky. Finally, if you go from a very vigorous exercise program to no exercise, or adopt a sedentary lifestyle, these choices increase your heart disease risk. This later finding is important. If you are a high-level exerciser then know that your atrial fibrillation risk is higher. However, there is a higher heart risk in stopping your vigorous exercise. The good news, to those that love to compete on a very high fitness level, is that if you reach a time when you transition to daily lower intensity programs up to 60 minutes a day or more, the risk may start to come down.

Walk. The final take home point is for everybody. As humans, we are largely designed to walk.

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ABOUT THE AUTHOR

T. Jared Bunch, MD

Dr. Bunch is a native of Logan, Utah and graduated from the University of Utah School of Medicine with alpha omega alpha honors. He completed internal medicine residency and fellowships in cardiovascular...read more

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